1. Field of the Invention
The present invention relates to an acoustic inspection method. In particular, it relates to an acoustic inspection system for a blemish on the surface of a disk (in particular, a stroke mark and the like in a contact-start-stop (CSS) inside a hard disk.
2. Description of the Related Art
There is available a type of hard disk, wherein the CSS area in which a head is standing by when a power source is off is provided over a disk. It sometimes happens that in the case of a hard disk provided with the CSS area, the head thereof comes into collision with the CSS area due to vibration and so forth taking place during transportation of the hard disk, thereby inflicting a stroke mark on the disk.
FIG. 7 is a schematic illustration showing a relationship between a height of a stroke mark left in the CSS area of the hard disk and a height of the head. The figure shows that the head 101 has a height of 30 nm to 80 nm from the surface of the disk 100 when levitated by rotating the disk 100 while a stroke mark 103 has a height in the order of 15 nm to 50 nm. Such a stroke mark can not be discovered by an ordinary read-while-write check. The hard disk having the stroke mark as described will be susceptible to failure occurring in a few month time from the start of actual use due to dust and the like which will be generated when the head 101 collides with stroke mark 103.
Although the stroke mark as described above can be discovered by opening up the hard disk, a product value of the hard disk once opened up will be depreciated because dust and the like can be mixed therein. Accordingly, a procedure for inspection that can be conducted without opening up a hard disk has been highly desired.
Meanwhile, there are techniques as disclosed in Japanese Patent Laid-Open No. H4-283421 and Japanese Patent Laid-Open No. H10-206340, which are applicable to a method of checking a blemish on the surface of a disk in the process of manufacturing a hard disk.
The techniques described are to detect directly vibration of an arm by fixing a mechanism for inspecting the vibration to the arm to which the head is attached, thereby deciding whether or not a blemish has been inflicted on the basis of the vibration.
However, since the conventional inspection method as described above requires a mechanism for inspecting the vibration, it takes time and cost to manufacture the mechanism. Further, the conventional inspection method can not be applied to hard disks already in widespread use. Furthermore, the described method is not applicable to inspection of fully fabricated hard disks because direct access to the arm is not possible once a cover for the hard disks is attached.
It is an object of the invention to detect a blemish on the surface of a hard disk (in particular, a stroke mark in the CSS area) without opening up the disk. Furthermore, it is intended that the invention not require extra labor or cost in fabrication of the hard disk, and is applicable to hard disks already in widespread use.
To this end, in accordance with a first aspect of the invention, there is provided an acoustic inspection method for hard disks, wherein an inspection for a blemish on a disk is conducted by picking a vibration occurring upon a head of a hard disk coming in collision with the blemish on the surface of the disk from a vibration propagating to a housing of the hard disk.
According to the first aspect of the invention, the inspection may be conducted during a period of time when driving of the disk is stopped, and the disk is in rotation by inertia.
In accordance with a second aspect of the invention, there is provided an acoustic inspection system for hard disks, comprising pickup means for picking up a vibration occurring upon a head of a hard disk coming in to collision with a blemish on the surface of the disk from a vibration propagating to a housing of the hard disk.
According to the second aspect of the invention, the pickup means may be a contact microphone.
Further, according to the second aspect of the invention, the pickup means may be is an optical head.
Still further, according to the second aspect of the invention, there may be provided means for amplifying the vibration picked up by the pickup means in the form of sound, and outputting the same externally.
Yet further, according to the second aspect of the invention, there may be provided a display for displaying the vibration picked up by the pickup means as a waveform.
Further, according to the second aspect of the invention, there may be provided storage means for converting the vibration picked up by the pickup means into digital values, and storing the same.
According to the second aspect of the invention, and with the features described above, there may be provided detection means for detecting a sound caused by the head of the hard disk coming in collision with the blemish on the surface of the disk on the basis of the vibration stored by the storage means.
Still further, according to the second aspect of the invention, and with the foregoing features, the detection means may have functions of controlling a power source for the hard disk, monitoring a condition of vibration, and varying an amplification factor of a sound to be outputted externally.
Yet further, according to the second aspect of the invention, and with the foregoing features, the detection means may have a function of notifying an observer of a time at which the disk is ready for inspection.
Further, according to the second aspect of the invention, and with the foregoing features, there may be provided means for applying a wavelet transform to the vibration converted into the digital values.
Still further, according to the second aspect of the invention, and with the foregoing features, the detection means may slice a time region immediately before rotation of the disk comes to a stop on the basis of the vibration stored by the storage means, and may carry out an analysis for the blemish in the CSS area of the disk.
Yet further, according to the second aspect of the invention, and with the foregoing features, the detection means may carry out an analysis for the blemish on the surface of the disk by use of a ratio of peak levels of acoustic data to average levels thereof.
Further, according to the second aspect of the invention, and with the foregoing features, the detection means may carry out an analysis for the blemish on the surface of the disk by use of the periodicity of peak levels appearing in acoustic data, and the deceleration characteristic of a spindle of the hard disk.
Still further, according to the second aspect of the invention, and with the foregoing features, the detection means may be capable of storing parameters for a plurality of types of hard disks, and carrying out an analysis for the blemish on the surface of the disk by use of parameters corresponding to respective types of hard disks to be inspected.
Yet further, according to the second aspect of the invention, and with the foregoing features, there may be provided a storage means for storing at an inspection acoustic data in an original sound condition.
In accordance with a third aspect of the invention, there is provided a program medium storing a program whereby an analysis for the blemish on the surface of the disk is carried out by use of a ratio of peak levels of the acoustic data to average levels thereof on the basis of vibration propagating to the housing of the hard disk, or an analysis for the blemish on the surface of the disk is carried out by use of the periodicity of the peak levels appearing in the acoustic data, and the deceleration characteristic of the spindle of the hard disk.
Finally, according to the first aspect of the invention, the inspection may be conducted in a reduced-pressure chamber.